The present invention relates to software supported methods, systems and tools used in the design and fabrication of custom parts which are machined on a CNC lathe, as well as to automated fixturing of such parts using a bushing.
Computer Numerical Control machining, or “CNC” machining, has become a prevalent way to machine high accuracy parts and injection molds. In certain applications, considerable work has been accomplished to automate the process for writing CNC machining instructions, using a CAD file provided by a customer which defines the shape of the part to be made. Considerable work has also been accomplished in providing quotations for parts machined or molded using those CNC machining instructions. Examples of such applications are explained in U.S. Pat. Nos. 8,239,284, 8,295,971, 8,140,401, 7,957,830, 7,840,443, 7,836,573, 7,630,783, 7,590,466, 7,574,339, 7,496,528, 7,299,101, 7,123,986, 7,089,082, 6,836,699 and 6,701,200, all assigned to the assignee of the present invention and all incorporated by reference. In the examples disclosed therein, the CNC machining was most commonly performed on a three-axis CNC mill. When the machining is to create an injection mold, the exterior-generally-rectangular-prism-shape of the mold is not defined by the customer's CAD file, so fixturing to hold the mold block during machining is relatively trivial. In contrast, when “total profile machining” is performed in the three-axis CNC mill so as to directly machine a part, fixturing is often an issue. See in particular U.S. Pat. Nos. 7,836,573, 7,840,443, 7,957,830 and 8,239,284.
While many (if not all) of the teachings of these incorporated-by-reference patents are equally applicable to both three-axis CNC milling and CNC lathe machining, there are many parts for which CNC lathe machining is more efficient than three-axis CNC milling. In a three-axis mill, the stock is held stationary relative to a high-speed rotating tool, whereas in a lathe the stock is rotated at high speed relative to a low-speed moving tool. Generally, parts which have cylindrical or circular profiles about a characteristic longitudinal axis are more efficiently machined using a CNC lathe than using a CNC three-axis mill. Lathe machining can increase efficiency both in terms of the cost of stock material (i.e., less waste), in terms of the duration of machining required, and in terms of reduced tool wear of that machining.
A common issue in lathe machining of a part is that while the part is being held at one end/rotated by the chuck, the cutter cannot cut the portion of the part that is in contact with or closest to the chuck. To be able to cut the portion of the part in contact with or closest to the chuck, a skilled machinist often first creates a custom fixture. The machinist then needs to take the workpiece out of the chuck, flip the orientation of the workpiece, put it in the fixture, and have the chuck hold the fixture/part from its opposite end.
Fixturing methods can be devised which are better suited for lathe machining than using the prior art fixturing methods which are equally applicable to three-axis milling. The present invention is particularly intended to capitalize on increased efficiency obtained by automated CNC lathe machining of certain parts.